[Xen-users] live migration time increases when using "mem-set"

["Tim Wood" <twwood@xxxxxxxxx>]

Hi,
I'm noticing very strange behavior when I create a VM, reduce its
memory allocation using "xm mem-set" and then live migrate it.

I would expect reducing the memory allocation would make the migration
occur faster, but instead I am seeing the opposite.

For example, if I create a VM with 900MB of ram initially, these are
the times I measure for different reduced memory allocations:

RAM (MB) - Migration length (sec)
900 - 11
768 - 20
512 - 33
450 - 38
256 - 51
128 - 55

Just the opposite of what I would expect!

As reference, if a VM is created with 256 MB of ram and migrated, that
takes about 4 seconds.

The VM is idle and so is the gigabit network.

Looking at the xend.log files it looks like I am getting hundreds of
lines like this:
ERROR (XendCheckpoint:227) netbuf race: iter 4, pfn 28f78. mfn ffffffff

I am using xen-testing... I'm very curious if this still occurs in
xen-unstable but can't test that myself right now.

-Tim

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